Method for cutting the flanks of an infeed worm and worm milling machine

ABSTRACT

Feed screws are used for container filling machines in order to separate a series of approaching containers at a specific distance from each other. Feed screws for non-rotationally symmetrically shaped containers are milled with a milling tool rotating at a high rpm, the shaft of which is arranged parallel to the longitudinal axis of the feed screw that rotates at a lower rpm. To avoid feed screw flank errors, the rotating milling tool is moved up and down in an oscillating manner, so that a milling tool can be used, the contours of which agree exactly with the associated cross sectional area of the containers which are to be handled. The first shaft of the milling tool is attached to a sliding carriage, which is movably guided in an upward and downward direction by means of a crank mechanism.

BACKGROUND OF THE INVENTION

The invention relates to a method for milling the flanks of a feed screwand to a feed screw milling machine.

Feed screws of the type under consideration are used in containerfilling machines such as, for example, bottle filling machines, in orderto position a series of approaching containers at a specific distancecorresponding to the respective incremental machine spacing. For thispurpose, such feed screws are also arranged between successive stationsof a filling machine, so that the containers are transferred at apredetermined distance from each other.

In order to transfer the containers, which generally either have nodistance or only a small distance between themselves, to the feed screw,a spiral groove is milled into the feed screw, the pitch of the flanksof which varies along the length of the feed screw and, in thisparticular case, in such a manner that the pitch increases from thepoint where the containers enter the feed screw toward the point ofexit.

The spiral shaped groove is milled into a feed screw blank by means of amilling tool that rotates at high rpm, with the feed screw blankrotating at a much lower rpm, while either the milling tool or the feedscrew is moved at variable speed in the axial direction. If the feedscrew which is to be produced is intended for use in the handling ofrotationally symmetrical containers, the rotating milling tool isarranged relative to the feed screw blank in such a way that the shaftof the milling tool extends at a right angle with respect to thelongitudinal axis of the feed screw blank. The milling tool has a linearmilling edge and mills the spiral shaped grooved independent of theinstantaneous feed screw pitch with the required precision and withoutflank errors, so that the production of a feed screw for rotationallysymmetrical containers is largely free of problems.

However, if the feed screw is intended for use in handling containersthat are not rotationally symmetrical, it should then have a spiralshaped groove with a cross sectional area that is suited to thecontainer which is to be handled. In order to mill the spiral shapedgroove in this case, the arrangement is configured such that the shaftof the milling tool extends parallel to the longitudinal axis of thefeed screw blank.

If the milling tool has a shape that precisely agrees with theassociated cross sectional area of the container shape that is to behandled, then, as a result of a changing pitch when the groove ismilled, there is an increasingly greater feed screw flank error as thepitch increases, that is, the spiral shaped groove becomes narrower asthe pitch becomes increasingly larger, whereby the crooked positioningor even a crushing of the containers can occur. This feed screw flankerror presently is corrected by employing a specifically oversizedmilling tool, but has the disadvantage that the spiral shaped groovethat is milled-in only agrees with the shape of the container which isto be handled at a very specific pitch. But at any of the other areasalong the feed screw the containers are not grasped and transferred inan error free manner, since the pitch usually increases in the directionfrom the start of the feed screw toward the end.

A further feature of the invention is the development of a method formilling the flanks of a feed screw of the type considered, such that theoccurrence of an error at the feed screw flank with variable feed screwpitch is avoided to the greatest degree possible Additionally, a feedscrew milling machine should be specified whereby a groove specificallydefined for the associated cross section of a container shape which isto be handled can be milled into a feed screw blank without theappearance of an error in the flank of the feed screw at variablepitches.

SUMMARY OF THE INVENTION

In the method according to the invention, the rotating milling tool ismoved up and down during the milling procedure. This entails theconsequence that the milling tool forms the contour of the containersgrasped later by the feed screw, whereby the occurrence of thepreviously common flank error is avoided, so that a milling tool can beused which has a contour that agrees with the associated cross sectionalarea of the containers which are to be handled. The containers arethereby grasped and transferred in an error free manner along the entirerange of the feed screw, so that a smooth work-sequence is assured inthe area of the feed screw.

In order to protect the milling machine and the feed screw blank, and toincrease the working precision, it is further recommended that thespiral shaped groove be initially pre-milled, preferably by twosuccessive milling procedures without an oscillation of the milling tooland, following that, a third milling procedure is carried out with anupward and downward directed oscillation of the milling tool. The thirdmilling procedure hereby only has the task of eliminating flank errorsproduced by the first two milling procedures.

According to the invention, it is recommended that the rotating millingtool be moved up and down at a rate of 7 to 8 dual-strokes per second,while the milling tool rotates at 3,800 to 4,000 rpm.

With a feed screw milling machine according to the invention, the shaftof the milling tool is attached to a sliding carriage which is arrangedso as to be movable upward and downward on a guide at a right angle tothe longitudinal axis of the feed screw. The oscillating movement of thesliding carriage is advantageously generated by a crank mechanism drivenby a motor. The stroke of the carriage should be about 60 mm in bothdirections, if the feed screw which is to be worked has the usualdiameter. The sliding carriage is preferably composed of cast aluminum,resulting in a relatively low weight.

If the shaft of the milling tool is driven by means of a belt drive,preferably by a toothed belt drive, which is the usual case, then,according to the invention, it is recommended that a first toothed beltconnects a first toothed pulley that is driven by a motor to anintermediate toothed pulley, which drives a third toothed pulley that isattached to the shaft of the milling tool by means of a second toothedbelt, and that the intermediate toothed pulley is arranged on a movablysupported second sliding carriage. This second sliding carriage shouldbe movably guided in a forward and reverse direction relative to thefeed screw at a right angle to the travel of the first sliding carriage.This design has the advantage that the toothed belt drive can closelyfollow the stroke movement of the first carriage without excessivelystretching the toothed belt. Since the intermediate toothed pulley cancorrespondingly follow the respective movement of the first slidingcarriage by means of a horizontal sliding movement of the second slidingcarriage, a corresponding stretch of the associated second toothed beltis almost completely avoided, while the first toothed belt onlyexperiences slight stretching with the movement of the second carriage,which lies within permissible limits.

The invention suggests, with considerable advantage, that the slidingcarriage along with the milling tool, the crank mechanism and theaccessory belt drive are attached to a framework which is supported soas to be swiveled around an axis which is at a right angle to thelongitudinal axis of the feed screw, whereby this swivel angle should be90°. Hence, the shaft of the milling tool can be swiveled from aposition parallel to the longitudinal axis of the feed screw, and into aposition that is at a right angle to this, which it assumes in order tomill a feed screw for handling rotationally symmetrical containers.Thus, the feed screw milling machine according to the invention can beused for producing both types of feed screws, whereby the millingprocedure for the groove corresponding to the rotationally symmetricalcontainers obviously takes place without an oscillating movement of themilling tool.

The respective work position for the swiveling framework can belocked-in pneumatically. For this, it is recommended that apneumatically actuated locking pin with a tapered head section enterinto a correspondingly shaped recess in the swiveling framework. If theframework is to be swiveled into the other work position, the lockingpin is pulled back out of the recess in the framework.

A more detailed description of a preferred embodiment of a feed screwmilling machine and the new milling method will now be set forth inreference to accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sketch explaining the method according to theinvention;

FIG. 2 is a lateral schematic view of the feed screw milling machine;

FIG. 3 is a front view of the milling machine according to FIG. 1;

FIG. 4 is a top view of the milling machine; and

FIG. 5 is an enlarged view of the pneumatic locking procedure for theswiveling framework of the milling machine.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a diagrammatic sketch, on the basis of which the methodaccording to the invention will now be explained. R in FIG. 1 representsa solid cylindrical blank which is composed of, for example, plastic. Atthis point, a flank pitch is to be milled into the blank for theproduction of a feed screw for containers. Milling the blank is carriedout by means of a milling tool S, which can be applied to the blank andis driven at a high rpm around the shaft 2. The blank rotates around theaxis A_(R) in a clockwise or counter clockwise direction. The shape ofthe milling tool S is determined by the shape of the containers that areto be transported later by the feed screw. If the shaft 2 of the millingtool is applied to the blank, the milling tool S mills a depression thatcorresponds to the milling tool. The shaft 2 thereby extends parallel tothe axis A_(R) of the blank. The blank R is supported for rotation by aspindle 30 that bites into an end of the blank. Spindle 30 is drivenrotationally by a headstock 31. The opposite end of the blank R issupported on a centering pin 32 which extends from a tailstock 33. Acoordinated relative movement of the milling tool S on the one hand andthe blank R on the other, in the extended direction of the axis A_(R) orthe shaft 2, causes the milling of the appropriate flanks with thedesired, varying pitch. According to the invention, during this millingprocedure the shaft 2 of the milling tool S now oscillates in thedirection of the arrow P_(auf) (up) P_(ab) (down) upward and downward,which leads to the consequence that feed screw flank errors are avoided,since the blank, at each position and independent of the pitch,possesses the appropriate width for the containers which are to betransported.

A feed screw milling machine with which such a milling method can beimplemented will now be specified, based on FIGS. 2 to 5. The actualmilling machine is represented in these figures, while the installationfor rotatably grasping (chucking) the feed screw blank R which is to beworked is not illustrated. The milling machine, as FIG. 2 showsschematically, includes three drive motors: drive motor 1 for the shaft2 of the milling tool S shown in FIG. 1, drive motor 3 for a crankmechanism 4, and drive motor 5 for swiveling a framework 6 around anaxis 7. The drive motor 5 is connected to the mechanism that causes therotation of 8. The shaft 2 of the milling tool is rotatably supported ina sliding carriage 9. The sliding carriage 9 on the one hand is arrangedso as to be movable in an upward and downward direction on a guide 10,so that the sliding carriage causes the upward and downward movement ofthe milling tool S as indicated in FIG. 1 b P_(auf) (up) and P_(ab)(down). For this purpose, the sliding carriage 9 is articulated with thelower end of the crank mechanism 4. The upper end of the crank mechanismis eccentrically articulated with a disk 11 (see also FIG. 3). The diskis driven by the drive motor 3. This drive motion moves the crankingmechanism for the sliding carriage 9 upward and downward, whereby themilling tool is also, in addition to the rotating movement occurringaround the shaft 2, moved in an oscillating manner upward and downward.

The drive motor 1 serves to drive the milling spindle 2. For this, thedrive motor is connected with an intermediate toothed pulley 13 by meansof a toothed belt 12, said intermediate toothed pulley being connectedto a toothed pulley so as to be driven by a second toothed belt 14, saidtoothed pulley 15 in turn being attached to the shaft 2 of the millingtool. The second toothed belt 14 extends at an approximate 90° anglerelative to the first toothed belt 12 as represented in the restingposition in FIG. 1. The intermediate toothed pulley 13 is attached to asecond sliding carriage 16. This sliding carriage in turn rests on aguide 17 and is arranged in this guide so as to be horizontally movablein a forward and reverse direction. To place the toothed belt 14 undertension, a U-profile 18 with oblong holes which are not illustrated ingreater detail, and into which set screws 19 can extend, is provided.The part 18 also connects the toothed pulleys 13 and 15. The toothedbelt 12 has initial tension applied by tightening a nut 20, whereby asupport mounting 21 for the intermediate toothed pulley 13 is swiveledaround an axis 22, on which the support mounting 21 that articulateswith the sliding carriage 16 is connected.

If the disk 11, on which the crank mechanism 4 is eccentricallyconnected, is rotated with a rotating shaft 2, the crank mechanism, asexplained, generates an upward and downward oscillating motion for thesliding carriage 9 and the shaft 2 attached to it with the milling tool,which is attached so as to be exchangeable in a slot 23 in the shaft(see FIG. 3). The stroke movements of the sliding carriage 9 would inand of itself lead to a stretching of the toothed belt 14, since theshaft 2 is not moved back and forth in a circular fashion around theaxis of the intermediate toothed pulley 13, but rather is moved up anddown linearly in a vertical direction by means of the sliding carriage9. Since, however, the sliding carriage 16 is movably supported alongthe guide 17 in the horizontal plate, the sliding carriage is moved tothe right by the pulling force generated by the upward and downwardmovement of the shaft 2 over the U-profile 18 in FIG. 2 with eachdeflection movement, so that the toothed belt 14 does not undergo achange in length. The displacement of the sliding carriage 16 with theintermediate toothed pulley 13 mounted on it only leads to a slightstretching of the toothed belt 12, but it can be selected such that itremains within permissible limits.

The framework 6, onto which the crank mechanism 4 with the associateddisk 11, the sliding carriage 9, the shaft 2 and its drive are fastened,is articulated so as to swivel on a fixed framework 24, whereby thecenter point of the shaft 2 and of the slot 23 for receiving the toollie on the swivel axis 7. By swiveling the framework 6 by 90°, the shaftis swiveled from its horizontal position into the vertical position, inwhich the feed screws for rotationally symmetrical containers are milledwithout oscillation.

In the respective work position of the swiveling framework 6, apneumatically actuated locking pin 25 with a conically tapered headsection 26 enters into a correspondingly shaped recess 27 in theswiveling framework 6, in order to lock it into the work position (FIG.5).

I claim:
 1. A method of milling the flanks of feed screws comprising the steps of:rotating a feed screw blank about its longitudinal axis at a relatively low rotational speed, rotating a milling tool at a substantially higher rotational speed about an axis of rotation which is parallel to the longitudinal axis of the feed screw blank and bringing the milling tool into contact with the blank while concurrently causing relative movement between the feed screw blank and the milling tool at a variable speed in the direction of the longitudinal axis, and concurrently oscillating the rotating milling tool perpendicularly to the longitudinal axis of the lead screw blank.
 2. The method according to claim 1 wherein prior to milling with said milling tool oscillating, performing the steps of:pre-milling by two successive milling procedures without oscillating the milling tool and then milling with the milling tool oscillating as aforesaid.
 3. The method according to any one of claims 1 or 2 wherein the milling tool is oscillated at a speed of seven to eight times per second.
 4. A feed screw milling machine comprising:means supporting a feed screw blank for rotating about its longitudinal axis, a first shaft and means for driving the first shaft rotationally about its longitudinal axis, a milling tool mounted on said shaft and the axis of the shaft is positioned for being in parallelism with the longitudinal axis of a feed screw blank, a first carriage on which said first shaft is supported for rotation and a guide on said machine for guiding the first carriage to oscillate up and down perpendicular to said axis of the feed screw blank, and means for oscillating said first carriage.
 5. The feed screw milling machine according to claim 4 wherein said means for oscillating said first carriage comprises:motor means mounted to said machine, and a crank mechanism interconnected between said motor means and said first carriage for oscillating said first carriage.
 6. The feed screw milling machine according to claim 4 wherein said first carriage oscillates through a distance of approximately 60 mm.
 7. The feed screw milling machine according to any one of claims 4, 5 or 6 including:a drive motor mounted to said machine and a first toothed pulley driven by said drive motor, an intermediate pulley and a first toothed belt coupling the first toothed pulley in driving relation to said intermediate pulley, a second carriage and means supporting said second carriage for sliding, said intermediate toothed pulley being mounted for rotating on said second carriage, a third toothed pulley fixed on said first shaft for the milling tool, and a third toothed belt coupling said intermediate pulley in driving relation to said third pulley.
 8. The feed screw milling machine according to claim 7 wherein said second carriage is guided by moving bidirectionally perpendicularly to the line of travel of said first carriage.
 9. The feed screw milling machine according to any one of claims 5 or 6 including:a frame comprising the machine and carrying said first carriage and said crank and the pulleys and belts for driving said first shaft, said frame being supported for swiveling 90° about an axis which is perpendicular to said longitudinal axis of said feed screw blank.
 10. The feed screw milling machine according to claim 9 including locking means and a pneumatic actuator for actuating said locking means to lock said frame in a selected working position into which said frame is swiveled.
 11. The feed screw milling machine according to claim 10 wherein said locking means comprises a lock bolt having a conically tapered head section for registering in a correspondingly shaped recess in said frame to prevent swiveling by said frame. 